1. Field of the Invention
This invention relates to the field of electrical cable coupling and shielding, and in particular to a data bus coupling arrangement of the type including a transformer and isolation resistors for electrically coupling together three or more data buses.
2. Description of Related Art
Data bus coupling arrangements are known which permit coupling of multiple high frequency data buses via transformers and isolation elements such as resistors. An example of such a coupler is disclosed in copending U.S. patent application Ser. No. 482,707, filed Feb. 21, 1990. This application describes a data bus coupler which includes a rigid housing for enclosing the coupling components. The coupler housing is overbraided to provide a continuous uninterrupted shield over the entire coupler, while nevertheless reducing its size in comparison with couplers having a rigid or solid shield.
Despite the advantages of the overbraided data bus coupler, it would in many instances be desirable to provide an even more compact coupling arrangement, while still providing complete protection from electromagnetic interference and environmental degradation.
Conventionally, the data bus cables are themselves each shielded by a metallic outer braid, providing excellent protection from interference. The problem to be overcome is that, at the point where the individual conductors are attached to the conventional coupler, shielding discontinuities may be present. The smaller the coupler, the more difficult it is to control such discontinuities.
Prior to the overbraided coupler, in order to overcome the problem of shielding discontinuities at data bus coupler terminations, and at cable joints in general, rigid metallic casings were provided as part of, or for enclosing, the coupler housings. The shielding casings were soldered or otherwise electrically connected to the cable braids and provided a measure of shielding continuity. However, such casings suffered the disadvantages of relatively high cost and large size.
In the overbraided data bus coupler, size is reduced by providing a flexible braid over the rigid data bus coupler housing. The housing, however, is retained to protect the delicate coupling components from physical damage. While clearly an improvement over prior art arrangements, further size reductions in the size of the overbraided coupler were limited by the need to provide a housing for the coupling.
As will become apparent from the following description of the invention, a rigid coupler housing is not necessary, and coupler size can be reduced without sacrificing protection of the coupler components from physical shocks, environmental degradation, or electromagnetic interference.